The Bergius process is a method of production of liquid hydrocarbons for use as synthetic fuel by hydrogenation of high-volatile bituminous coal at high temperature and pressure. It was first developed by Friedrich Bergius in 1913. In 1931 Bergius was awarded the Nobel Prize in Chemistry for his development of high pressure chemistry.
The coal is finely ground and dried in a stream of hot gas. The dry product is mixed with heavy oil recycled from the process. A catalyst is typically added to the mixture. A number of catalysts have been developed over the years, including tungsten or molybdenum sulfides, tin or nickel oleate, and others. Alternatively, iron sulphides present in the coal may have sufficient catalytic activity for the process, which was the original Bergius process. There are also considerations with respect to global warming, especially if coal liquefaction is conducted without carbon capture and storage technologies.
The mixture is pumped into a reactor. The reaction occurs at between 400 and 500 °C and 20 to 70 MPa hydrogen pressure. The reaction produces heavy oils, middle oils, gasoline, and gases. The overall reaction can be summarized as follows:
- (where x = Degrees of Unsaturation)
The immediate product from the reactor must be stabilized by passing it over a conventional hydrotreating catalyst. The product stream is high in naphthenes and aromatics, low in paraffins and very low in olefins. The different fractions can be passed to further processing (cracking, reforming) to output synthetic fuel of desirable quality. If passed through a process such as Platforming, most of the naphthenes are converted to aromatics and the recovered hydrogen recycled to the process. The liquid product from Platforming will contain over 75% aromatics and has a Research Octane Number (RON) of over 105.
Overall, about 97% of input carbon fed directly to the process can be converted into synthetic fuel. However, any carbon used in generating hydrogen will be lost as carbon dioxide, so reducing the overall carbon efficiency of the process.
There is a residue of unreactive tarry compounds mixed with ash from the coal and catalyst. To minimise the loss of carbon in the residue stream, it is necessary to have a low-ash feed. Typically the coal should be <10% ash by weight. The hydrogen required for the process can be also produced from coal or the residue by steam reforming. A typical hydrogen demand is ~80 kg hydrogen per ton of dry, ash-free coal. Generally, this process is similar to hydrogenation. The output is at three levels: heavy oil, middle oil, gasoline. The middle oil is hydrogenated in order to get more gasoline and the heavy oil is mixed with the coal again and the process restarts. In this way, heavy oil and middle oil fractions are also reused in this process.
The most recent evolution of Bergius' work is the 2-stage hydroliquefaction plant at Wilsonville AL which operated during 1981-85. Here a coal extract was prepared under heat and hydrogen pressure using finely pulverized coal and recycle donor solvent. As the coal molecule is broken down, free radicals are formed which are immediately stabilized by absorption of H atoms from the donor solvent. Extract then passes to a catalytic ebullated-bed hydrocracker (H-Oil unit) fed by additional hydrogen, forming lower molecular weight hydrocarbons and splitting off sulfur, oxygen and nitrogen originally present in the coal. Part of the liquid product is hydrogenated donor solvent which is returned to Stage I. The balance of liquid product is fractionated by distillation yielding various boiling range products and an ashy residue. Ashy residue goes to a Kerr-McGee CSDA unit which yields additional liquid product and a high-ash material containing unreacted coal and heavy residuum, which in a commercial plant would be gasified to make the H2 needed to feed the process. Parameters can be adjusted to avoid directly gasifying any of the coal entering the plant. Alternative versions of the plant configuration could use L-C Fining and/or an antisolvent deashing unit. Typical species in the donor solvent are fused-ring aromatics (tetrahydronaphthalene and up) or the analogous heterocycles.
Friedrich Bergius developed the process during his habilitation. A technique for the high-pressure and high-temperature chemistry of carbon-containing substrates yielded in a patent in 1913. In this process liquid hydrocarbons used as synthetic fuel are produced by hydrogenation of lignite (brown coal). He developed the process well before the commonly known Fischer-Tropsch process. Karl Goldschmidt invited him to build an industrial plant at his factory the Th. Goldschmidt AG (now known as Evonik Industries) in 1914. The production began only in 1919, after World War I ended, when the need for fuel was already declining. The technical problems, inflation and the constant criticism of Franz Joseph Emil Fischer, which changed to support after a personal demonstration of the process, made the progress slow, and Bergius sold his patent to BASF, where Carl Bosch worked on it. Before World War II several plants were built with an annual capacity of 4 million tons of synthetic fuel. These plants were extensively used during World War II to supply Germany with fuel and lubricants.
The Bergius process was extensively used by Brabag, a cartel firm of Nazi Germany. Plants that used the process were targeted for bombing during the Oil Campaign of World War II. At present there are no plants operating the Bergius Process or its derivatives commercially. The largest demonstration plant was the 200 ton per day plant at Bottrop, Germany, operated by Ruhrkohle, which ceased operation in 1993. There are reports  of the Chinese company constructing a plant with a capacity of 4 000 ton per day. It was expected to become operational in 2007, but there has been no confirmation that this was achieved.
During World War II the United States conducted secret research in converting coal to gasoline at a facility in Louisiana, Missouri. The Louisiana operation began about 1946 using captured German technology. Located along the Mississippi river, this plant was producing gasoline in commercial quantities by 1948. The Louisiana process method produced automobile gasoline at a price slightly higher than, but comparable to, petroleum-based gasoline but of a higher quality. The facility was shut down in 1953 by the Eisenhower administration, allegedly after intense lobbying by the oil industry.
- Bergius, Friedrich (May 21, 1932). "Chemical reactions under high pressure" (PDF). Nobel Foundation. Retrieved 2009-01-23.
- Takao Kaneko, Frank Derbyshire, Eiichiro Makino, David Gray, Masaaki Tamura and Kejian Li "Coal Liquefaction" in Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH, doi:10.1002/14356007.a07_197.pub2
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-  Archived March 19, 2005, at the Wayback Machine.
- China's first coal liquefaction scheduled to ease import burden, UPDATED: 10:28, January 24, 2005, People's Daily Online
- Energy Policy in America since 1945
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- The Early Days of Coal Research, U.S. Department of Energy webpage